On a nine-point scale, each additional unit of hog odor was associated with increases of 0.23 mm Hg in diastolic blood pressure and 0.10 mm Hg in systolic blood pressure, according to Steve Wing, PhD, of the University of North Carolina at Chapel Hill, and colleagues.

Likewise, each 1 parts-per-billion increase in the concentration of hydrogen sulfide – which has a rotten egg smell – was associated with elevations of 0.12 mm Hg in diastolic and 0.29 mm Hg in systolic blood pressure, the researchers reported online in Environmental Health Perspectives.

"If the associations were causal, and if malodors from other sources such as sewage, landfills, and chemical refineries produce similar effects, then control of environmental malodor might help prevent repeated acute elevations of blood pressure that could contribute to development of chronic hypertension," Wing and colleagues wrote.

Industrial swine operations emit a plethora of smelly chemicals, including ammonia, hydrogen sulfide, and hundreds of volatile organic compounds created in animal confinement buildings, waste storage areas, and use of animal waste as fertilizer.

Exposure to bad smells and pollutants has been associated with self-reported stress and altered mood in previous studies.

The current study evaluating blood pressure included 101 nonsmoking adults living in one of 16 neighborhoods located within a mile and a half of at least one industrial swine operation in the eastern coastal plain region of North Carolina, a major center for swine production.

Half of the participants were older than 53, and most (84%) identified themselves as black.

Twice a day for about 2 weeks, the participants sat outdoors for 10 minutes, recording the intensity of hog odor, stress levels, and other factors in a diary. When they went back inside, they measured their own blood pressure using an oscillometric automated device.

At the same time, the researchers measured ambient levels of hydrogen sulfide and particulate matter at a central location in each neighborhood.

After adjustment for time of day, particulate matter was not related to blood pressure, but hog odor and hydrogen sulfide concentrations were.

The researchers estimated that diastolic pressure was almost 2 mm Hg higher when hog odor was most intense and that systolic pressure was almost 3 mm Hg higher when hydrogen sulfide concentrations were at their highest.

The magnitude of the effects "could have public health importance due to the frequency and duration of odor episodes near confined animal feeding operations," the authors wrote.

Blood pressure was strongly associated with self-reported stress levels, with an average increase of 0.82/0.57 mm Hg per unit increase on the stress scale.

Adjustment for stress attenuated the relationship between odor and blood pressure but had little effect on the association between hydrogen sulfide and blood pressure.

The authors said that the findings relating odor – but not particulate matter – to changes in blood pressure are consistent with a psychopathological mechanism.

"Odorant pollution could also produce other changes in a person's environment that cause acute changes in blood pressure; for example, irritability of a household member," they wrote.

They acknowledged some limitations of the study, including potential confounding by time-related changes in air pollution and blood pressure and possible measurement errors in blood pressure and hydrogen sulfide concentrations.

The study was conducted in partnership with the Concerned Citizens of Tillery, a community-based organization in Halifax County that promotes the health, environmental, and political interests of predominantly African-American communities in eastern North Carolina. It was funded by the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency.

Wing provided pro bono testimony in legal proceedings related to landfills and provided pro bono advice on radiation and health for a law firm that made a gift to the University of North Carolina and another law firm that did not make a gift to the University of North Carolina. He conducted research, funded by the Water and Environment Research Foundation, on symptoms reported by neighbors of areas where sewage sludge is applied to land.

Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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